2) To avoid putting users' DiskStation at risk, please don't paste links to any patches provided by our Support team as we will systematically remove them. Our Support team will provide the correct patch for your DiskStation model.

This post is meant as a warning to other users, more than an actual question!

Recently we upgraded one of our small VMware environments to vSphere 6. Soon to experience crashed LUNs and even crashed disks. After two weeks and two disaster recovery scenarios, we decided to go back to vSphere 5.5 as this has been running flawlessly for a long time.

Our environment:
Three DELL R620 servers and two Synology RackStations - One RS3412RPxs and one RS3614RPxs. All Synos are running DSM 5.2 with newest patches. All LUNs are configured as Block-Level iSCSI Targets.

Our experience when running vSphere 6:
When the ESXi host starts up, we see two paths to each LUN on the Syno with LUN IDs like 0, 1, 2, etc. But after a while, the host has quadrupled the paths to each LUN with LUN IDs like 0/256/512/768, 1/257/513/769, etc. And when this happens, all the trouble starts. This is where the Syno gets so busy, that the LUNs are crashing (unrecoverable crashes).

Our conclusion:
After the storm has ceased, we did some investigation and in vSphere Configuration Maximums we found, that Maximum LUN ID has increased from 255 to 1023 (8 bits vs. 10 bits respectively). This might explain the extra "modulus 256" LUNs that the Syno starts to present (numbere 256/512/768 etc.).

Hello, we have same issue.
We had to disable path to "ghost" luns, but they become active after some time again. So we changed round robin to fixed manage path policy. Now it`s fine. Waiting for some fix from VMware or Synology.

Any answer from Synology support? After host reboot disabled "ghost" path sometimes become active again and i have to check it on each host. When "ghost" path is in enable state my DS1513+ become very very slow. Need fix from Synology.

cheplyaev.av wrote:Any answer from Synology support? After host reboot disabled "ghost" path sometimes become active again and i have to check it on each host. When "ghost" path is in enable state my DS1513+ become very very slow. Need fix from Synology.

Thursday July 2nd we received the following response to our Synology Support Ticket #609013.

Thank you for your feedback and sorry for this late response.
We are really appreciated for your information, our developers have looking into this issue now.
For now, please use ESXi 5.5 as workaround now, we will sort this out as soon as possible.
Hope this has and please let us know if any further assistance.

Take care and have a good day,
Technical Support
Ricky Lu

To me, this sounds like Synology has almost accepted this to be a problem. However we haven't heard anything from them since.